Negative Search Engine Optimisation is the name in the Search Engine Optimisation (SEO) / industry for when someone makes an attempt to lower a website's rankings in search engines by various means, both legal and illegal.
If you are working in a locality where Google dominates the search engine market (like the UK), the GOOG Webmaster Guidelines (https://support.google.com/webmasters/answer/35769) might be considered the laws of the land for the SEO industry. For example, GOOG offers us multiple tools to help us do 'Negative SEO' on sites which violate these rules by reporting issues.
I recall one ex-Googler saying in a Q&A at a conference that all Webspam reports are read by a human being - I don't know if the same goes for Map spam. Google's Juan Felipe Rincon stated in 2016 that Google takes action on 65% of user-generated spam reports (http://searchengineland.com/google-takes-action-on-65-of-user-generated-spam-reports-243708).
Part of a SEO strategy report can include competitor analysis, including analysing competitors' sites looking at where they are getting 'good quality' backlinks from with the aim of trying to obtain the same or similar links. You may notice some spammy links in this process. That said, don't expect (m)any spam reports to GOOG to have the desired outcome even if you report the (same) direct contravention of their rules on a regular basis! I've read a comment on a forum that “Submitting a complaint to Google about a spammer is like sending a letter to Santa Claus at the North Pole.” which is what it often feels like in my experience. Google may already be aware of the issue you are reporting so I'd recommend focusing on well-ranked profiles and sites. Reporting competitors' contraventions of Google Webmaster / Adwords guidelines might be considered just something you need be able to say you've done as part of your ongoing work for your SEO / PPC clients.
The following activities (in theory at least) of analyses of competitors' compliance with search engine, social media site and legal guidelines can create real competitive advantage & might also be considered by some to be a cornerstone of retained SEO / PPC activity.
To this day, Google is not very good at detecting all the sites which:
It's fundamental to know that any links intended to manipulate Google PageRank (http://en.wikipedia.org/wiki/PageRank) or a site's ranking on Google may be considered part of a link scheme and thus be a violation of Google’s Webmaster Guidelines. This includes any behaviour that manipulates links to your site or outgoing links from your site.
The following is just one example of a link scheme which may negatively impact a site's ranking in search results if Google take action:
Other links may be part of a paid 'Featured Promotion', labelled as such or as an
'Advertorial' & 'Sponsored Content' and multiple permutations of these phrases. Searching for these phrases in relation to your client's non-branded key phrases may help identify these links.
Here is Google's guidance on link schemes: https://support.google.com/webmasters/answer/66356?hl=en and some guidance from Google's Webpspam Team (headed by Matt Cutts) on how to write actionable web spam reports: http://googlewebmastercentral.blogspot.co.uk/2010/11/how-to-help-google-identify-web-spam.html.
In short, in my experience Google is better at identifying low quality links than high quality links. (there is no way your client or yourself can be identified publicly as the reporter of paid links).
So in brief,
Other webmaster guidelines / website terms worth scrutinising competitor's compliance with include the following:
https://www.linkedin.com/legal/user-agreement ( a professional services search engine)
Note that PO Boxes or mailboxes located at remote locations are not acceptable business addresses. Report competitors' violations here: https://support.google.com/maps/answer/3094088.
Send general feedback (with screenshot if need be) – this may be necessary for Map spam via https://support.google.com/maps/answer/3094045
Also if you find a review of / by a competitor that you think violates Google review policies, (https://support.google.com/plus/answer/2622994) you can use the “Flag as inappropriate” link next to a review. https://support.google.com/business/answer/4596773?hl=en.
https://www.cap.org.uk/Advice-Training-on-the-rules/Advice-Online-Database/Video-blogs-Scenarios.aspx) which apply across media including online (including social media channels) state that ads & marketing ‘must be obviously identifiable as such’ e.g. with an identifier on Twitter such as the hashtag “#ad”. See https://www.cap.org.uk/Advice-Training-on-the-rules/Advice-Online-Database/Remit-Social-Media.aspx. It's possible to report any any of your competitors' social media marketing content not labelled appropriately to the ASA. This may have the additional 'benefit' of helping to 'blacken' their online reputation if the results of a successful complaint are published.
5. Report competitors' Google Adwords policy contraventions:
Also there's https://topcontributor.withgoogle.com, https://www.google.com/local/guides/ & the little-known army of unpaid volunteers, called Mappers (who propose and approve edits to Google Maps, with an assist from Google employees), these are all ways of Google getting free labour from SEO consultants / the general public.
They should compensate this work in some way! Gis a job ;)
It's arguable that the above tools that may enable you to 'harm' your competition are a double edged sword. If as a result of your reporting a whole sector appears to be using practices against a certain set of guidelines, in theory your own site / practices may come under scrutiny too!